Beam loss and collimation in the Fermilab 16 GeV proton driver Page: 1 of 3
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Jt Fermilab
WVFERMILAB-Conf-01/128 July 2001
BEAM LOSS AND COLLIMATION IN THE FERMILAB 16 GEV PROTON
DRIVER*
A. I. Drozhdint, O. E. Krivosheev, N. V. Mokhov, FNAL, Batavia, IL 60510, USA
AbstractA high beam power of 1.15 MW in the proposed 16-GeV
Proton Driver [1] implies serious constraints on beam losses
in the machine. The main concerns are the hands-on main-
tenance and ground-water activation. Only with a very effi-
cient beam collimation system can one reduce uncontrolled
beam losses to an allowable level. The results on tolerable
beam loss and on a proposed beam collimation system are
summarized in this paper. A multi-turn particle tracking in
the accelerator defined by all lattice components with their
realistic strengths and aperture restrictions, and halo inter-
actions with the collimators is done with the STRUCT code
[2]. Full-scale Monte Carlo hadronic and electromagnetic
shower simulations in the lattice elements, shielding, tun-
nel and surrounding dirt with realistic geometry, materials
and magnetic field are done with the MARS 14 code [3]. It
is shown that the proposed 3-stage collimation system, al-
lows localization of more than 99% of beam loss in a special
straight section. Beam loss in the rest of the accelerator is
0.2 W/m on average.
1 TOLERABLE BEAM LOSS
To determine tolerable beam loss, MARS 14 simulations
are done in the arc cells. Regulatory requirements [4] are
taken as the limits to be met. A detailed lattice descrip-
tion with dipoles, quadrupoles and long bare beam pipes
has been implemented into a 3-D model with correspond-
ing materials and magnetic field distributions (see Fig. 1). A
16-GeV proton beam is assumed to be lost on a beam pipe at
a grazing angle of 1 mrad inward. It is distributed uniformly
along the arc lattice. Results are normalized per 1 W/m
beam loss rate, that corresponds to 3.9x 108 p/(m-sec). In
this simplified model, a round 2-m radius tunnel with the
beam line in the center is assumed with a 0.4-m concrete
wall followed by a NuMI-like dirt [4]. The later, probably,
gives the worst-case situation for ground-water activation.
The allowable losses can be noticeably higher in dolomite
or the Fermilab Booster location. Dose accumulated in the
hottest spots of the coils, residual dose rates on the outer sur-
face of the lattice elements after 30 days of irradiation and
1 day of cooling, and ground-water activation and dose at-
tenuation in the surrounding dirt are calculated.
Maximum residual dose rates calculated for the arc ele-
ments at 1 W/m uniform beam loss are shown in the third
column of Tab. 1. The table gives also the peak dose
accumulated in the coils and the parameter Ctot calcu-
lated according to [4]. The last column gives correspond-
* Work supported by the Universities Research Association, Inc., under
contract DE-AC02-76CH03000 with the U. S. Department of Energy.
t drozhdin@fnal.gov-----
Figure 1: A fragment of the MARS model of the arc.
ing beam loss rates calculated to meet the limits of [4]:
Py=100 mrem/hr, D=20 Mrad/yr and Ctot=1. The dose
near the bare beam pipes exceeds the design goal for hot re-
gions of 100 mrem/hr; it is noticeably lower near the mag-
nets due to significant absorption of soft photons in the
dipole and quadrupole materials. One sees that hands-on
maintenance is a serious issue with about 3 W/m as a tol-
erable maximum beam loss rate in the lattice elements, ex-
cept for the long bare beam pipes where one should de-
crease the loss rate to 0.25 W/m to reduce the dose to
100 mrem/hr. One needs further reduction to bring the dose
down to a good practice value of about 10-20 mrem/hr.
Alternatively, one can think of providing simple shielding
around the bare beam pipes. For ground-water activation
Ctot=0.975 immediately outside the 40-cm tunnel wall, that
allows 1.03 W/m beam loss rate. The peak accumulated
dose in the coils is about 2 Mrad/yr at 1 W/m beam loss rate.
Table 1: Peak residual dose P, on lattice elements, dose D
in the coils, parameter Ctot and allowable beam loss.
Value Element Peak Allowable
at 1 W/m loss (W/m)
Long pipe 400 0.25
P Quad side 9.4 10.6
(mrem/hr) Quad flange 34 2.94
Dipole side 5 20
Dipole flange 20 5
D (Mrad/yr) Coil 2 10
0tot Ground water 0.98 1.03
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Alexandr I. Drozhdin, Oleg E. Krivosheev and Nikolai V. Mokhov. Beam loss and collimation in the Fermilab 16 GeV proton driver, article, July 20, 2001; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc715293/m1/1/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.